The term "water-swellable polymeric networks" as used herein refers to highly crosslinked polymers which have a propensity to swell or gel in the presence of water. Water-swellable polymeric networks have found wide use in a variety of applications. See, for example, Odian, G., Principles of Polymerization, 3rd Edition, published by. Wiley-Interscience, New York, 1991 and Glass, J. E., Ed. "Polymers in Aqueous Media Performance Through Association," Advances in Chemistry Series 223, published by the American Chemical Society, Washington, D.C., 1989).
Water-swellable polymeric networks which are well known in the polymer arts include, but are not limited to, carboxymethylcellulose, crosslinked polyacrylates, graft copolymer hydrolysis products of starch-acrylonitrile, polyvinyl alcohol resins, polyethylene oxide resins and polyacrylonitrile resins.
Several problems are associated with such polymeric networks. First, their water absorbency properties are greatly reduced in the presence of salts, such as sodium chloride, which are often present in the environments where such polymeric materials are used. Second, most of these polymeric materials are not readily biodegradable and thus contribute to the overall chemical burden on the environment when they are released into effluent streams.
Some crosslinked polypeptides containing a high percentage of anionic amino acids, such as aspartic acid or glutamic acid, are useful as super absorbing materials. Some of these are disclosed in International Patent Publication WO 92/17525 and in U.S. Pat. No. 5,284,936 to Sikes, et al. Such materials have improved saline absorbency and are biodegradable. However, they require amino acids as starting materials and these are relatively expensive.
Koskan, et al. in U.S. Pat. Nos. 5,057,597, 5,116,513, 5,219,952 and 5,221,733 describe inexpensive methods for the manufacture of polysuccinimide and polyaspartic acid. The chemical modification of polysuccinimide to produce useful polyaspartates is well known. For example, Neri, et al., in the article, "Synthesis of alpha, beta-Poly[(2-hydroxyethyl)DL-aspartamide], a New Plasma Expander," Journal of Medicinal Chemistry, Vol. 16, pp 893-897, (1973) describe the modification of polysuccinimide with ethanolamine.
Fujimoro et al. in U.S. Pat. No. 3,846,380 describe the formation of modified polypeptides having hydrophobic and hydrophilic substituents as side chains obtained by reacting polysuccinimide with at least one primary or secondary aliphatic amine and hydrolyzing the resulting polyamide derivative with alkali to produce polypeptides that are useful as surface active agents.
There is still a need and desire, therefore, for biodegradable, super absorbing polymeric networks with improved saline tolerance preparable by an economical method. This invention satisfies that need.